We will continue our program of synthesizing more potent estrogen synthetase (aromatase) inhibitors and of evaluating the more promising ones as anti-fertility agents. We have prepared one inhibitor in radioactive form and will use this to investigate metabolism, uptake and elimination. Several aromatase inhibitors we have tested attenuate the proestrus estrogen and LH surges in the rat and block mating and ovulation as well. We now will attempt to obtain additional evidence that the mechanism of action of these compounds is induced by estrogen deprivation. We also are interested in how estrogen acts in various reproductive processes. We have designed experiments to use aromatase inhibitors to provide some of this information. BIBLIOGRAPHIC REFERENCES: Further studies with Aromatase (Estrogen Synthetase) Inhibitors for Fertility and Mammary Tumor Control. A.M.H. Brodie, D.A. Marsh, J.-T. Wu and H.J. Brodie. Endocrinol. 98, Meeting Abstract, June, 1977. Fertility Regulation by an Aromatase (Estrogen Synthetase) Inhibitor Using Silastic Implants. H.J. Brodie, A.M. Brodie, J.-T. Wu and D.A. Marsh. Society for the Study of Reproduction, Meeting Abstract, Austin, 1977.